This does come up on occasion. Could be the processor or the power supply. Last one I saw the power supply board was going bad and could not provide good voltage to the processor when it warmed up. I do think this would be repeatable on your home layout though.
A test might be smoke on vice off. Also, it could be a bad smoke fan motor, but a bad motor would have immediate effect. Yours sounds thermal, which points to a board issue.
Swap your power supply board between a good engine. IF the symptom follows the PS board that is the issue. G